The present application relates to U.S. patent application Ser. No. 09/491,769 entitled xe2x80x9cHydraulic Energy Recovery Devicexe2x80x9d filed Jan. 26, 2000, and U.S. patent application (Attorney Docket No OKL-0118PA) entitled xe2x80x9cMethod And Apparatus for Boosting Interstage Pressure In A Reverse Osmosis Systemxe2x80x9d, each of which are hereby incorporated by reference.
The present invention relates generally to a reverse osmosis systems suitable for desalinization of water, and more specifically, to a recirculation system and concentrate energy recovery in a reverse osmosis system.
Reverse osmosis (RO) is a process widely used for desalinization of water. Reverse osmosis membranes are contained in a process chamber into which pressurized feedwater is admitted. A portion of the pressurized water permeates across the membrane and exits the process chamber as purified water at a low pressure and is referred to as permeate. The remainder of the water, still at high pressure, exits the process chamber and is referred to as a concentrate.
During the life of a membrane the fluid pressure must be adjusted slightly to ensure optimum operation. Without such optimization, the system becomes inefficient. It some systems it is often necessary to recirculate a portion of the concentrate through the same membrane to obtain a desirable flow velocity within the membrane for optimal performance.
Referring now to FIG. 1, a known reverse osmosis system 10 is illustrated having a feed pump 12 which is driven by a motor 14 to pressurize feed fluid from a feed input 16. Pressurized fluid leaves pump 12 through an output 18, travels through a valve 19 and enters a first reverse osmosis process chamber 20. The process chamber 20 has a permeate header 22 through which permeate is removed from the reverse osmosis chamber 20. Reverse osmosis chamber 20 also has a concentrate output 24 which removes concentrate from the reverse osmosis chamber 20 at a high pressure. The concentrate output 24 is coupled to a valve 26 through which a portion of the concentrate enters the feed stream upstream of feed pump 12. The remaining concentrate passes through valve 28.
One problem with devices such as those illustrated in FIG. 1 is that they are very inefficient. The concentrate pressure is typically about 30 psi less than the pressure entering reverse osmosis chamber 20. The feed pressure, however, may approach, for example, 1000 psi or higher. Thus, the flow passing through control valve 26 undergoes a substantial pressure reduction from about 970 psi to about 30 psi in the present example. Thus, feed pump 12 must pressurize the recirculation flow as well as the feed flow.
Another known arrangement similar to FIG. 1 is illustrated having the same components illustrated with the same reference numerals. In this embodiment, a pump 30 driven by a motor 32 couples concentrate at an elevated pressure above that of the feed stream.
One problem with these types of systems is that although they are more energy efficient than other known systems, energy dissipated in control valve 28 cannot be recovered. Another drawback to this type of system is that recirculation pump 30 is expensive because of the high working pressure. Another drawback to the system is that the motor 32 consumes a substantial amount of energy.
It is therefore one object of the invention to provide a reverse osmosis system that uses concentrate recirculation to allow the membrane to operate efficiently while recovering otherwise wasted energy.
In one aspect of the invention a process chamber preferably a reverse osmosis chamber, has a feed inlet, a low pressure outlet, and a high pressure outlet. A feed pump is used to increase the pressure of feed fluid to feed inlet.
A common shaft is used to rotatably couple a booster and an energy recovery turbine together. The energy recovery turbine is fluidically coupled to the high pressure outlet to drive the booster pump. The booster pump is positioned between the feed pump and process chamber and increases the pressure of feed fluid.
In a further aspect of the invention, a method for operating a reverse osmosis system comprises the steps of:
boosting a pressure of fluid output from a feed pump prior to entering to a first process chamber using from a first portion of a high pressure fluid from a high pressure outlet of a first process chamber;
recirculating a second portion of the high pressure fluid; and
fluidically coupling the second portion of the high pressure fluid between the feed pump and the process chamber.
One advantage of the present invention is that energy-wasting throttle valves and bypass lines have been eliminated from the reverse osmosis process. Another advantage of the invention is that more energy is recovered from the process lowering the overall cost of operating such a process. Another advantage is that the components can be combined into a single package.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.